Biosphere 2 Center

Exercise 12: Fire-based Restoration of Biodiversity in Ecosystems Dominated by Nonnative Grasses
Module 12: Disturbances: Geological and Contemporary

This exercise is a field practical, to be used to demonstrate the field skills you have thus far acquired in the class.

Introduction

(Reference citations are included at the bottom of the webpage)

As nonnative species continue to increase in distribution and abundance, so do their effects on indigenous species. Increases in some nonnative species have reduced or eliminated indigenous plants and animals, and thereby contributed to permanent changes in diversity and species composition (e.g., Bock et al. 1986, OTA 1993). These types of changes have consequential implications for ecosystem function (Naeem et al. 1996). In the southwestern United States, establishment and spread of nonnative Lehmann lovegrass (Eragrostis lehmanniana Nees) and Boer lovegrass (Eragrostis chloromelas Steud.) appear to be disrupting native ecosystem processes at multiple spatial and temporal scales. Prescribed fire has been proposed as a restoration tool in these semi-arid systems, even though considerable evidence suggests that fires enhance establishment of these nonnative lovegrasses (e.g., Cable 1965, 1971, Ruyle et al. 1988, Sumrall et al. 1991, Robinett 1992, Biedenbender and Roundy 1996). Because increased abundance of nonnative lovegrasses likely is detrimental to some native species and to overall biological diversity, we have initiated an experimental assessment of the influence of fire regime on abundance of nonnative lovegrasses and biological diversity. Our specific objectives are to (1) determine effects of fire season on responses of biotic communities along a continuum of invasion by lovegrass, and (2) quantify relationships between biological guilds before and after burning and through recovery.

Our experiment is taking place within grasslands and Prosopis savannas at the Fort Huachuca Military Reservation (FHMR) (31º 34’ N, 110º 26’ W) in the Huachuca Mountains of southern Arizona. Elevations range from 1420 to 1645 meters and two-thirds of the annual 440 mm of precipitation falls between July-October and 20% falls December-March. A hot, dry period between late March and early July prior to the onset of the monsoon season characterizes this region. Since 1977 fire history has been recorded on FHMR; some areas have not burned during this period, while other areas have burned as frequently as every year. Livestock have been excluded from FHMR since 1950.

We have developed and scheduled a randomized-block design with a full-factorial treatment structure. Extant plant community is a blocking factor (see plot selection below) and burn season is the treatment (spring fire, summer fire, no fire). We are using a 1-ha plot size, which is large enough to minimize edge effects and to allow adequate sampling of the plant, invertebrate, and small mammal communities.

We identified 3 types of grasslands, representing a continuum of invasion by nonnative species:
· Grasslands dominated by the nonnative grass Eragrostis lehmanniana
· Native-dominated grasslands with Aristida spp., Bothriochloa barbinodis, Bouteloua spp., Digitaria californica, Eragrostis intermedia, and Panicum spp.
· Grasslands composed of a mix of nonnative and native species.

In the summer of 1999, we chose 18 sets (blocks) of sites at FHMR, 6 within each of these 3 types of grassland community. Within each block we established 3 1-ha plots. Each of the 3 plots within a block will receive 1 of 3 fire treatments. We will treat plots at 9 of the 18 sites in 2001 and plots at the other 9 sites in 2002 for a total of 3 replicates per community type (n = 3) per treatment (n = 3) in a given year (n = 2). We marked the corners of 54 plots with metal fence posts and recorded coordinates using a global positioning system (GPS) to ensure the plots could be relocated.

We measured plant biomass in 25, 1 m x 0.5 m quadrats in each plot. Vegetation was clipped 2.5 cm above the ground and separated into species. Samples were oven-dried to constant weight at 65 ºC. We determined total biomass and calculated species richness and diversity using these data.

· Additionally, we marked and measured every mesquite (Prosopis velutina) and juniper (Juniperus deppeana) on all 54 plots.

In May and August 2000, we trapped small mammals and invertebrates in 27 plots (9 blocks). We sampled small mammals using an 8 X 8 grid of Sherman folding traps (12-inch, ventilated) (64 traps per plot) for 5 days. We marked captured animals with ear tags and secondary color markings.

We sampled invertebrates using pitfall traps in a 3 X 3 grid (9 traps per plot) for 24 hours.

Between April and September 2000 we counted birds seen and heard in 170-m radius variable circular plots overlapping treatment plots on FHMR.

To estimate nesting success and to assess the influence of environmental factors on nest fate we searched for and monitored the fate of nests at FHMR. Nests were found by rope dragging, pole sweeping, behavioral observations of adult birds.

We are also measured vegetation both at nest sites and in randomly located plots within each variable circular plot. These data will be used to examine vegetation associations for nesting birds and for additional species detected in point counts.

Lecture

Lecture will describe the types of disturbances that have historically occurred and that continue to date. These disturbances structure ecosystems for great periods of time after they occur, in proportion to their magnitude. Therefore, understanding how they occur and their impact is important for conservation biology 

Students will be asked at the end of the lecture to begin thinking of how to answer the question: "How successful are the different fire regimes used in the Fort Huachuca Project in restoring native biodiversity?" All relevant background information is provided above. Consult with your TA and instructors if you have specific questions about the site or the project that are not answered above.

Objectives

1. Understanding of the role of fire frequency and intensity in structuring ecosystems.
2. Grasp that disturbances are essential for the maintenance of many desert ecosystems.
3. Understanding of the scientific method.
4. Knowledge of some of the abiotic factors that influence plant diversity.
5. Knowledge of basic biology of desert perennials including their scientific names.

Skills

1. Ability to create, execute, analyze, and present an entire research project, when given only the research question and location within which to work
2. Ability to standardize data collection across different environmental conditions
3. Demonstrated dexterity with the field equipment that we've used to date
4. Familiarity with the origins of measurement field error and how to minimize it.
5. Skill in conducting collaborative group research projects
6. Be able to integrate data into a coherent story
7. Improved ability to present work orally

Methodology

• Question: How successful are the different fire regimes used in the Fort Huachuca Project in restoring native biodiversity?
• Possible Independent Variables: To be determined by class
• Dependent variables: To be determined by class
• After lecture and once we have arrived onsite to FHMR, the students will walk around the field site and begin to collaboratively formulate a research design that would best answer the question
• You do not need to incorporate GIS or GPS into the exercise, but you are encouraged to do so if the technology necessary for them is present on site.
• Best design that adequately answers the question will be that which we follow as a class
• In the afternoon, after spending the morning coming up with ideas, the students will go to the field and begin experimenting with the best way to sample the necessary data. If it is possible to begin collecting data in the afternoon, that should be started
• At night we will discuss the design and further refine the question, hypotheses, methodology, data analysis, and expected results.
• Early in the morning of the second day, we will collect all needed data, completing all field work by 10 AM. Late morning and early afternoon will be spent processing and analyzing the data
• Present the work as an oral report at the end of the day in the form of a PowerPoint presentation, if the technology necessary for that is available on site. Otherwise, use more traditional modes of scientific communication, such as a talk with printed or drawn visual aids.

References

*Biedenbender, S.H., and Roundy, B.A.  1996.  Establishment of native semidesert grasses into existing stands of Eragrostis lehmanniana in southeastern Arizona.  Restoration Ecology 4:155-162.
 

*Bock, C.E., Bock, J.H., Jepson, K. L., and Ortega, J. C.  1986.  Ecological effects of planting African lovegrasses in Arizona.  National Geographic Research 2:456-463.
 

*Cable, D.R.  1965.  Damage to mesquite, Lehmann lovegrass, and black grama by a hot June fire.  Journal of Range Management 18:326-329.
 
*Naeem, S., Thompson, L.J., Jones, T.H., Lawton, J.H., Lawler, S.P., and Woodfin, R.M.  1996.  Changing community composition and elevated CO2.  Pages 93-100 in Korner, C., and Bazzaz, F.A. (editors), Carbon Dioxide, Populations, and Communities.  Academic Press, San Diego.
 

*Office of Technology Assessment.  1993.  Harmful non-indigenous species in the United States.  OTA-F-565, U.S. Government Printing Office.  Washington, D.C.
 

*Robinett, D.  1992.  Lehmann lovegrass and drought in southern Arizona.  Rangelands 14:100-103.
 

*Ruyle, G.B., Roundy, B.A., and Cox, J.R.  1988.  Effects of burning on germinability of Lehmann lovegrass.  Journal of Range Management 41:404-406.
 

*Sumrall, L.B., Roundy, B.A., Cox, J.R., and Winkel, V.K.  1991.  Influence of canopy removal by burning or clipping on emergence of Eragrostis lehmanniana seedlings.  International Journal of Wildland Fire 1:35-40.

Authors: G. R. McPherson, R. J. Steidl, E. Albrecht, E. Geiger, A. Litt, J. Danoff-Burg
Revision date: 31 May 2001